1. Field of the Invention
The present invention relates to the fields of immunology and cancer therapy, and is directed to biological compositions and methods for inducing human monocytes to a cytoxic state. The invention concerns the purification and characterization of soluble factors, and particularly, of peptides, which induce human monocyte cytotoxicity and have utility in anti-cancer therapy.
2. Description of the Related Art
Immune protection of vertebrates is provided by a dual system that maintains two basic defenses against foreign invaders. These two defenses, termed cellular and humoral immunity, are adaptive and respond specifically to most foreign substances, although one response generally is favored. While cellular immunity is particularly effective against foreign tissue, cancer cells, intracellular viral infections and parasites, the humoral immune response defends primarily against the extracellular phases of bacterial and viral infections. Therefore, the cellular response is directed primarily against invading cells, while the humoral response is directed against primarily cell products, such as toxins. Moreover, whereas cellular immunity is provided by cells of the lymphoid system, humoral immunity is provided by proteins called antibodies that circulate through the fluid compartments of the body.
The dual nature of the immune system is generated from two separate populations of morphologically indistinguishable lymphoid cells called lymphocytes. While one class of lymphocytes, the T-cell lymphocytes, mediates the cellular immune response, the other class of lymphocytes, the B-cells, is responsible for the humoral immune response. Thus, when the organism is invaded by a foreign substance, for example an altered cell (e.g. viral transformed cell or tumor cell), some of the T-cells that recognize it are activated and initiate reactions that include binding to and eliminating the altered cells. On the other hand, when individual B-cells are activated, they differentiate to plasma cells that secrete specific antibodies directed against substances secreted by the foreign invader. For a review of the foregoing, see Hood et al., (Immunology, Second Edition, Benjamin/Cummings Publishing Company, Inc., Menlo Park, Calif., 1984).
While cells of B-lymphocyte lineage have found widespread clinical and industrial application in the generation of monoclonal antibodies, cells of T-lymphocyte lineage have proved of interest in part due to the numerous soluble factors they secrete. In the biological system, T-cell factors play an important role in modulating and activating various immune functions. Isolation and characterization of various T-cell factors has been the goal of many clinical research endeavors attempting to identify those factors which might be useful in treating a number of disease states, for example, in the treatment of tumor cells and viral infectious states. Of particular interest has been the recent characterization of a factor termed T-cell growth factor, or interleukin II, which is produced and secreted by effector T.sub.A cells. (See U.S. Pat. Nos. 4,401,756; 4,404,208; 4,407,945; and 4,473,642). When T.sub.C cells are stimulated by interleukin II, they undergo an effector phase and are stimulated to mature into killer T-cells which are capable of identifying and eliminating various target cells. As demonstrated by the above patents, interleukin II has become an important pharmaceutical agent in the treatment of various disease states.
Optimism spurred by the preliminary success of interleukin II has lead researchers on a quest to identify other immune-mediating factors having potential clinical applicability. However, this search has generally been hampered by the existence of numerous factors secreted by the same or similar cell types. Moreover, confusion often results from the general overlapping nature of the factor activities and often times from a lack of currently available test systems for identifying individual factor activities. Without highly sensitive test systems for identifying individual factor activities, the existence of a particular factor cannot be readily distinguished from other factor activities.
Recently, interest has been shown in identifying soluble factors which serve to stimulate human monocyte cytotoxicity. Monocytes are a phagocyte of the blood which, along with macrophages and polymorphonuclear leukocytes, bind and ingest foreign substances often prior to an antibody response. "Activated" monocytes have recently been shown to exert an antitumor activity. For example, Fischer et al. (Cell. Immunol., 58:426-435, 1981) disclose that human peripheral blood monocytes can reproducibly lyse a variety of tumor cells. More recently, researchers have disclosed various factors thought to play a role in monocyte activation. For example, Kleinerman et al. (Cancer Res., 45:2058-2064, 1985), discusses the activation of human blood monocytes by incubation with concanavalin A-stimulated lymphokine (macrophage-activating factor (MAF)), lipopolysaccharide endotoxin, and human recombinant gamma interferon. It was reported that gamma interferon, in the presence of endotoxin, was capable of activating monocyte tumoricidal activity. Moreover, MAF treatment exhibited a similar effect.
Other monocyte cytotoxicity promoting factors have been identified as well. For example, Le et al. (J. Immunol., 131:2821-2826, 1983) has reported a T-cell hybridoma line capable of producing a macrophage activating factor with the ability to activate human blood. Monocytes to show enhanced cytotoxicity against a human colon adenocarcinoma line. However, this activity was found to be neutralized with specific antiserum to purified human interferon-gamma. These authors concluded that this MAF was in fact interferon-gamma.
More recently, Jones and Clouse (Immunobiol., 167: Abstract No. 365, 1984) reported the use of lymphocytes from patients with Sezary's syndrome in the production of a human T-cell hybridoma line which is capable of producing a factor which stimulates human monocyte antitumor cytotoxicity. In contrast to the factor identified by Le et al., the factor reported in the Jones and Clouse publication was not inhibited by antibodies having specificity for interferon-gamma. Although the Jones and Clouse reference did observe that two molecular weight species having the biological activity was observable, the methodology used to identify this particular activity was not identified. Moreover, the methodology for identifying and isolating Sezary/T-cell hybridomas which secrete the particular factor was not disclosed. Clearly, not all Sezary/T-cell hybridomas are capable of producing monocyte stimulatory factors (See, e.g., Grillot-Courvalin et al., "Helper T-Hybridoma Produced By Fusion With Sezary Cells," in: T-Cell Hybridomas, ed. by M. J. Taussig, CRC Press, Inc., Boca Raton, Fla., 1985).
It is apparent from the foregoing references that, not only are there numerous factors potentially involved in the stimulation of human monocyte cytotoxicity, but additionally that these factor activities may be indistinguishable in previously available assays for detecting various cytotoxic actions. Moreover, as with other cytokines, the purification and characterization of monocyte cytotoxicity inducing factors has been hampered simply by their naturally low abundance in biological systems.
Accordingly, the present invention is directed to methods for accomplishing the isolation of particular discrete soluble factors which exhibit human monocyte cytotoxicity inducing activity. The present disclosure is further directed to the purification and characterization of these factors and to the preparation of T-cell hybridoma lines which produce these factors in vitro and thereby provide a ready source for isolating the factors. In that the novel factors of the present invention demonstrate a surprising ability to elicit an antitumor response by monocytes in vitro, similar to that possessed by interleukin II for lymphoid cells, it is believed that these factors will provide an important new addition to the antineoplastic armament of medical science.